Spark-gap.



F. W. PEEK, In.

SPARK GAP.

APPLICATION HLED AUG-l9, 191s.

Patented July 3, 1917.

Inventor: FranK Peek. Jr, y Mp His flttorneg.

UNITED STATES PATENT OFFICE.

FRANK W. PEEK, JR., OF SCHENEC'IADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SPARK-GAP.

Specification of Letters Patent.

Patented July 3, 191 '7.

Application filed August 19, 1915. Serial No. 46,398,

To all whom it may concern:

Be it known that I, FRANK W. PEEK, Jr, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Spark- Gaps, of whichthe following is a specification.

My invention relates to lightning arresters of the type having a sparkgap for relieving transmission lines and other conductors of transientvoltages and similar abnormal conditions.

Transient voltages, surges, and other abnormal conditions on theconductor of a transmission line or piece of electrical apparatus imposesevere strains on the various dielectrics, such as air and insulation,which adjoin the conductor. To relieve these strains spark gaps are usedand are so set that the dielectric of the spark gap will withstand thestress of normal voltage on the conductor but will rupture and permit adischarge to ground when subjected to some higher voltage. The voltageat normal frequency at which spark over or complete dis charge occurs isusually called the breakdown voltage of the gap. If a transient voltagerises at about the same rate as the normal voltage at normal frequency,that is, the front of the wave of transient voltage is not much steeperthan the front of a wave of normal voltage, the dielectric of the sparkgap will rupture before the transient voltage can rise very much abovethe breakdown voltage. To rupture any dielectric, whether gaseous,liquid or solid, energy must be expended in the dielectric and thereforea time element or time lag is introduced into the action of the sparkgap. On account of the time lag, the application of a voltage whichrises at a very rapid rate, as for example, a transient impulse, doesnot cause a spark gap constructed in the usual manner to spark over orcompletely break down at the instant the break down voltage is reached.The voltage overshoots or continues to rise above the breakdown valueduring the period of time required to rupture the dielectric of thespark gap. The more rapidly the transient voltage is rising the greaterthe height it will attain during that period of time. In a spark gapconstructed in the usual manner, this period of time may be great enoughto permit a traveling wave to pass the spark gap and reach the stationapparatus, or a transient voltage with a steep wave front or a voltageimpulse may rise to a value far above normal before the gap breaks down.In some cases the wave form of the transient voltage may be such thatthe spark gap does not respond to it as readily as the insulationof'some of the apparatus, and the apparatus is injured before the sparkgap has time to discharge. This time lag seems to be due to the factthat in spark gaps constructed in the usual way, local break down, suchas brush discharge, or corona, first occurs in the path of the arc atsome lower voltage than spark over, or before spark over or completedischarge takes place.

The object of my invention is to provide a protective device which isfaster in action and more elficient than spark gaps constructed in theusual manner, particularly in responding to rapidly rising voltage suchas transient voltages and voltage waves with steep fronts. A furtherobject is to provide a protective device suitable for installation outof doors and practically unaffected by rain and changes of weather. Tothis end, I proportion and arrange the spark gap in such a manner thatthe air or other dielectrio is subjected to electrostatic stress in sucha manner that complete discharge or spark over occurs without any localdischarge such as brush discharge or corona in the path of the arc. Aspark gap constructed in accordance with my invention is more eflicientthan a spark gap constructed in the usual manner, as it is very muchfaster, will discharge very much more quickly and for a given linevoltage the electrodes can be set much closer together. The dielectricmay be stressed in the desired manner in various ways, but I have foundthat the best results are obtained if the electrodes of the spark gapare so proportioned and positioned with relation to each other that alarge part of the electrostatic stress between the proximal or nearestportions of the electrodes is so uniformly distributed that no localbreak Clown of the air, such as brush discharge or corona, occurs in theath of the arc prior to spark over or comp ete breakdown of the gap whenpotential is applied to the elec trodes. The desired distribution of theelectrostatic stress is best secured by the use of electrodes which havetheir coiiperating or proximal surfaces in the form of surfaces ofrevolution, such a cylinder or sphere. The electrostatic stress in thegap between such electrodes will be suiliciently uniform if the lengthof the gap is within certain definite limits, which depend upon the sizeand shape of the electrodes. For example, in air at atmospheric pressureat sea level, spherical electrodes should not be farther apart thanabout twice the radius of the sphere, else the gap will be slow. I havealso found that if the electrodes are placed too close together the gapwill be slow and inefficient. Spherical electrodes, for example, withair as the dielectric, should not be closer than three tenths of thesquare root of the radius of the sphere measured in centimeters andbetter results are obtained if the electrodes are separated at least onehalf of the square root of the radius of the sphere measured incentimeters. The exact spacing necessary to secure the best resultsdepends somewhat upon the density of the air. Ordinarily I prefer toconnect a spark gap constructed in accordance with my invention andhaving two electrodes properly placed with relation to each other asabove, in series with some current controlling means such as aresistance, an electrolytic cellor similar device. It is also desirablein some cases to associate with a sphere gap constructed in accordancewith my invention one or more gaps of different types connected inparallel with the sphere gap in order to minimize the efl'e'cts ofweather and other variable conditions on the protection afforded theconductor.

My invention will best be understood in connection with the accompanyingdrawing in which, merely for purposes of illustration, I have showndiagrammatically some of the various forms in which my invention may beembodied and in which Figure 1 is a diagram of a sphere gap constructedin accordance with my invention; Fig. 2 of a modified form of gapembodying my invention; Fig. 3 a diagram of a composite spark gapembodying my invention and proportioned to respond to practicall anyabnormal condition on the line, and ig. 4: is a diagram maticillustration of another modification, showing partly in longitudinalsection another form of high speed gap which responds very quickly toabnormal potentials.

In the particular form of device shown in Fig. 1, a conductor 1 such asa conductor of a transmission line has a discharge path through anelectrolytic cell 2 which for purposes of illustration is shownconnected to ground. In series with the cell and between it and theconductor 1 is a sphere spark gap constructed in accordance with myinvention and adapted for use in the air at sea level. This sphere gapcomprises two spherical electrodes 3 separated by an air gap 4, of whichthe length does not exceed the diameter of eitherof the spheres 3, butin air at sea level is greater than one third or one half the squareroot of the radius of either f them measured in centimeters. In practiceI prefer to make the spheres 3 the same size and make the gap t aboutequal to their radius. In some cases I may shunt the gap by a condenser5 while in other cases the condenser is omitted. In a sphere gapconstructed in this manner, the electrostatic stress between proximalsurfaces of the electrodes appears to be sufficiently uniform so that nolocal discharge such as brush discharge or corona, occurs in the path ofthe are between said surfaces prior to spark over and completedischarge. As a result thereis no appreciable time lag betweenapplication of break down potential and complete break down of the gap.If the electrodes 3 are spaced either farther apart or closer togetherthan the limits just mentioned, the complete break down of the gap ispreceded by local discharge in the path of the arc and the objectionabletime lag of the common forms of spark gap is present.

A sphere gap is not particularly efficient in extinguishing the arewhich follows the discharge through the gap, and therefore, I prefer touse the electrolytic cell 2 in series with it. As soon as the dischargethrough the gap 4 and the cell 2 to ground has reduced the potentia'lofthe line to normal the electrolytic cell 2 prevents further flow ofcurrent.

The shape of the electrodes of the gap may be modified in various waysbut the best results are obtained with electrodes which have theirproximal surfaces in the form of surfaces of revolution. The particularform which I prefer is the sphere. Whatever the absolute size of thesphere, the minimum time lag in air at sea level is obtained when thespacing between their proximal surfaces is between twice the radiusofthe sphere and one half of the square root of that radius measured incentimeters. In particular, the best results are obtained when thelength of the spark gap in air is about equal to the radius of thesmaller sphere. A horn gap which is set to have a much lower break down"oltage at normal frequency than the sphere gap may be connected inparallel with the sphere gap yet transient voltages with steep wavefronts will discharge through ,the sphere gap instead of the horn gap inspite of the higher break down Voltage of the sphere gap at normalfrequency.

A sufficiently uniform distribution of enough of the electrostatic fluxto eliminate a great deal of the time lag can also be obtained withelectrodes having substantially plane proximal surfaces. I prefer tomake such electrodes in the form shown in Fig. 2, in which theelectrodes 5 are in the form of disks having their edges curved to aradius sufficiently great to prevent formation of corona at the normalpotential of the line. As in Fig. 1, the gap is preferably connected inseries with an electrolytic cell 2 to prevent flow of current at normalpotential.

The break down voltage of a sphere gap at normal frequency is lowered,if the spheres become wet, and consequently the electrodes shouldpreferably be kept dry by a suitable housing. If the gap must be exposedto the weather, the spacing of the electrodes must be greater than Whereit is protected. I may provide a gap of a different kind in parallelwith the sphere gap to secure maximum protection under all conditions ofweather and to secure other desirable results For example, as shown inFig. 3, the main sphere gap 4: is connected in shunt with a horn gapcomprising two elongated electrodes 6 which approach each other closelyat points 7 intermediate their ends and diverge in both directions fromthese points to form a horn gap of the usual type. In some cases spheres8 or other electrodes having their proximal surfaces in the shape ofsurfaces of revolution are mounted adjacent the points 7 of the hornsand positioned with relation to each other to form a sphere gapembodying my invention. Where I use more than one gap, I may provideresistance between the electrodes of the different gaps. I may forexample, insert resistance 9 between each electrode 3 of the main spheregap and the corresponding electrode on the auxiliary gap. The horn gapis preferably mounted above the sphere gap in position to receive theare rising from the sphere gap. If an arc persists in the sphere gap itis transferred to the horn gap and broken by it. I may also associatewith the sphere gap a needle gap having pointed electrodes 10 in suchrelation to the horn gap that an arc in the needle gap is transferred tothe horn gap. I may also in some cases provide a condenser in shunt tothe sphere gap.

A combination of gaps as shown in Fig. 3 is desirable where the gaps areto be mounted out of doors, as wetting the electrode surfaces of a sparkgap lowers its spark over voltage to a greater or less extent dependingupon the electrodes. When the electrodes of the spark gaps shown in Fig.3 are wetted the normal spark over voltage of the horn gap is lowered toa lem extent than that of the sphere gap, while the change in normalbreak down or spark over voltage of the needle gap is very slight. Toprevent break down of the gaps at normal line potential when theelectrodes are wet by rain, for example, the spacing of the sphere gapmust be made greater than would be necessary were the spheres to remaindry: the horn gap spacing need be changed to a less extent; and theneedle gap spacing need be changed scarcely at all. In such acombination of gaps connected in multiple, and exposed to the weather,the same normal are over voltage for all the gaps when the electrodesare wet can be obtained only by setting the gaps so that when theelectrodes are dry, the normal spark over voltage of the sphere gap ishigher than that of the horn gap and also higher than that of the needlegap. Setting the gaps as above described makes a combination especiallysuitable for use out of doors, and with the advantage that a selectiveaction for different kinds of voltage waves is secured. The needle gapand horn gap have lower spark over voltages than the sphere gap forvoltage waves of normal or sloping wave fronts and will respond to thesevoltage waves, while higher voltage waves with steep wave fronts willdischarge through the sphere gap, in preference to the other gaps. Byusing a plurality of gaps of different characteristics and set to havedifferent normal spark over voltages, a marked selective action can beobtained.

This selective action for voltage waves of diflerent heights and wavefronts may also be obtained by nurling all or part of the surfaces ofthe electrodes of the sphere gap, as for example, by smoothing theproximal portions between which discharge occurs and roughing theremainder of the surfaces, by adding lugs or projections to theelectrodes or by otherwise modifying them.

In Fig. 4, I have shown diagrammatically another form of high speed gapcomprising electrodes 11 which have between them a member or body 12 ofporcelain or other insulating material in such a relation to theelectrodes that the path of discharge between the electrodes is alongthe surface of the'insulating body 12. I have found that the insulatingbody arranged as above described causes the electrostatic stress betweenthe electrodes ll to be distributed in such a manner that a voltageimpulse, a voltage wave with a steep front, will cause a dischargebetween the electrodes 11 with much less time lag than in the spark gapof the ordinary type. As shown in Fig. 4 a horn gap 13 may be connectedin parallel with the high speed gap and preferably in position to takeany are which forms in the high speed gap.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A protective device comprising two cooperating electrodes havingtheir proximal surfaces spherical and shaped apart to form a spark gapwhich resists normal potential and has a length not exceeding twice theradius of either spherical surface but greater than about three tenthsof the square root of said radius in centimeters.

2. A protective device comprising two spheres spaced apart a distancenot exceeding twice-the radius of said spheres but greater thansubstantially one half the square root of said radius in centimeters.

3. A protective device comprising two cooperating spherical electrodesseparated to forms, spark gap, two elongated electrodes mountedimmediately above said spherical electrodes and diverging to form ahorn-gap connected'in parallel with said spark gap and in the path-ofarc gases rising from said spherical electrodes, and a resistanceconnected between one of said spherical electrodes and one of saidelongated electrodes.

4:. The combination of two elongated electrodes mounted vertically andseparated at a point intermediate their ends by a spark gap, saidelectrodes diverging upwardly and downwardly from said gap, andauxiliary electrodes mounted below said gap and having their proximalsurfaces sphericaland-separated by a gap not exceeding twice the radiusof curvature of said surfaces and greater than about one half the squareroot of the radius in centimeters of said surfaces.

5. The-combination of a sphere gap having spherical electrodes separatedby a gap not exceeding twice the radius of each sphere and greater thanabout one half the square root of said radius in centimeters, aneedle-gap in parallel with said sphere gap and comprising pointedelectrodes immediately above said-sphere gap, and a horn gap in parallelwith said sphere gap and mounted above saidneedle gap, said gaps beingso set that when all are dry the are over voltage of said horn gap isless than that of said sphere gap and greater than that ofsaid needlegap.

6. A protective device for electric conductors comprising twocooperating elec- 8. A- protective device comprising a sphere gap havingspherical electrodes spaced apart-a distance not exceeding the diameterof either of said electrodes but greater than one half the square rootof the radius in centimeters of'either electrode, an electrolyticcell-in series with said gap and a condenser connected in shunt to saidsphere gap.

9. 'A high speed spark gap comprising two electrodes having between thema bridge of solid insulation'with its ends in contact with saidelectrodes and so shaped that the discharge path of minimum length isalong the surface of said insulation.

10. A -high speed spark gap comprising two electrodes and a cylindricalbridge of porcelain in the axis of said gap with its ends in contactwith'saidelectrodes to pro- I vide a discharge-path of minimum lengthalong the surface of said bridge.

Inwitness whereof, I have hereunto set my-hand'this 14th day of August,1915.

FRANK w. PEEK, JR.

Copies-of. this-patent may be obtained for-fivecents each; byaddressing'the "Commissioner-of Patents, Washington, iDJC.

